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Newsgroups: rec.crafts.metalworking
Subject: Re: Controlled Atmosphere Heat Treating Furnace
From: (J. Kimberlin)
Date: 21 Sep 1995 17:35:59 -0700

In article <>,
Andrew Mawson  <> wrote:
>>      I am planning in adding a small (electric) heat treat furnace to my shop.  Have been looking at the one
>> in Brownells catalog (about $500).  with about a 6" x6" x6" capacity.  Has anyone seen any other units in
>> this price range (or lower?).  Basically it needs to be capable of about 1600 degree operations.
>>      I would also like to run a small gas purge to the furnace to control oxidation, rather than using the
>> expensive stainless foil bag stuff.  Any ideas on what gas to use?  Dry nitrogen is cheap and plentiful, 
>> but I think I might have a problem with "nitriding" steel parts.  Is argon a problem also? (I don't want to use
>> any toxic or expensive gases.
>I would be VERY interested on comments regarding John's concern over danger of nitriding steel parts. Is
>this possible using nitrogen ? I understood ammonia gas was used which is not very neighbourly !
>I would dearly love to be able to nitride (ie surface harden at lowish temperatures) in my home workshop.
>To date I have been using case hardening compounds such as KASENIT, but these require red heat with
>consequent distortion.

Ammonia gas is not the only way to nitride things.  One can use potassium 
cyanide or sodium cyanide.  Here in California that is the way we nitride 
convicts at San Quentin - in viewing distance from my residence.

Trouble is, nitriding and case hardening are not quite the same thing, 
IMHO.  I have books in the company library that tell all of this and it 
is somewhat confusing.  I haven't worked through my confusion because I 
haven't had a need as yet.

Kasenit contains about 20% potassium ferricyanide and 80% something else 
that I haven't had a chance to analyze yet, but may be bone meal.  So it 
really does nitride stuff to some extent, in that the heat produces
hydrocyanic acid that attacks the surface of your workpiece.  Trouble is, it
does not give that wonderful mottled cyanide finish one sometimes sees on
the frames of fine firearms.

Potassium Cyanide is perfectly safe until you put acid on it.  Trouble 
is, most people shy away from melting potassium cyanide and dipping a 
very clean workpiece into it.  But that is what you do if you don't want 
to use ammonia and put up with its smell and explosive dangers.  All this 
is over and above the reaction of the authorities when they find out you 
are not a commercial regulated entity and have cyanide in your shop.


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